1. Field of the Invention
The present invention relates in general to a method of processing an intelligent network service call in an electronic switching system for Toll/Tandem, and more particularly to a method of processing a call requesting an intelligent network service such as a credit call service in which subscriber's information must be received in the middle of the service.
2. Description of the Prior Art
Recently, intelligent network services have been proposed for the purpose of meeting various requirements of communication service users. In the intelligent network services, a service switching point (referred to hereinafter as SSP) is provided to act as a barrier. Namely, the SSP analyzes a call from a subscriber of a telephone network and, upon determining that the subscriber call requires any one of the intelligent network services as a result of the analysis, requests a service control point (referred to hereinafter as SCP) as a service data base to transmit call control information necessary to the process of the corresponding intelligent network service. Then, the SSP performs the intelligent network service required by the subscriber in accordance with the call control information from the SCP.
In an electronic switching system for Toll/Tandem, there are provided a variety of intelligent network services in which subscriber's information must be received in the middle of the services. The representative one of the intelligent network services is a credit call service.
In the credit call service, an agreement on a credit number and a billing number is made between the subscriber and an operator. Upon a service request from the credit number, a call charge is automatically levied on the billing number specified by the service subscriber. This credit call service is convenient because the subscriber can telephone with no cash regardless of his position, only with the confirmation of a credit state. In order to protect the subscriber from a third person knowing the credit number of the subscriber, the credit call service requires the user to transmit a personal identification number (PIN) every telephone call. In this case, the credit call service will connect the telephone call from the user to a called number required by the user through a screening process.
By the way, in the intelligent network service such as the credit call service with a complex number system and procedure for use, the information can readily be collected using only an existing subscriber signalling method or a dual tone multi-frequency (referred to hereinafter as DTMF) method in the case where the SSP is disposed in a local exchange hierarchy. But, it is not efficient to dispose the SSP in all local exchanges in an initial provision of the intelligent network service, since there is little demand initially for the intelligent network service. Therefore, in the initial provision of the intelligent network service, the SSP is not disposed in any local exchange but in a TOLL hierarchy, so that the intelligent network service can be provided for all the initial users with a variation of information regarding the TOLL and no correction of the local exchange.
However, in the case where the SSP is disposed in the TOLL hierarchy, the use of a local exchange to which the user belongs and an inter-net trunk signal (R2 multi-frequency compelled, referred to hereinafter as R2MFC) is not suitable to the collection of all necessary information. Also, this makes it impossible to let the user hear of an announcement from the transit exchange. The reason is that there is no provision of a DTMF signalling method in the existing transit exchange which enables the existing transit exchange to communicate directly with the subscriber. Noticeably, to enable the existing transit exchange to communicate directly with the subscriber, a signalling method using a loop dial pulse may be provided separately From the DTMF signalling method using the multi-frequency.
For this reason, in the case where the SSP is disposed in the TOLL hierarchy, both the inter-net trunk signalling method (R2MFC) and the subscriber signalling method must be employed to collect the information necessary to the intelligent network service.